Elastomers can be crosslinked by a number of techniques as described by A. Coran in "Science and Technology of Rubber" Chapter 7. Most elastomers are cured using sulfur or peroxide vulcanization although curatives such as phenolic resins, quinone derivatives, maleimide derivatives and metal oxides can also be employed in the crosslinking reaction.
A novel crosslinking reaction was reported in Kautschuk Gummi Kunststoffe 8/83 which discloses a cure system consisting of the adduct of a diisocyanate with nitrosophenol. In this cure system, the nitrosophenol is released at cure temperature and reacts with the elastomer. Crosslinking occurs when the diisocyanate reacts with functionality on the polymer bound nitrosophenol. This blocked isocyanate curative is incorporated in a step separate from the polymerization.
Polymer bound isocyanates have been used as part of a curing package of acrylate polymers. European Patent Application Publication No. 130,322 discloses that acrylate polymers containing m-isopropenyl .alpha.,.alpha.-dimethyl benzylisocyanate (TMI) can be cured and that the polymers can be used in coating applications. U.S. Pat. No. 4,694,057 discloses that elastomers containing small amounts of 1-(1-isocyanato-1-methylethyl)-3-(1-methylethenyl)- benzene (TMI) can be crosslinked by utilizing difunctional or polyfunctional active hydrogen compounds. For instance, U.S. Pat. No. 4,694,057 discloses that elastomers which are difficult to cure with sulfur or sulfur containing compounds, such as polychloroprene, can be cured utilizing such a technique. However, neither the teachings of European Patent Publication No. 130,322 or U.S. Pat. No. 4,694,057 suggest any advantage that can be realized by blocking the isocyanate groups in the elastomer. In fact, neither of the subject references disclose the possibility of curing such compounds which contain blocked isocyanate groups. Problems associated with premature crosslinking have hindered the commercial development of cure systems which rely on crosslinking through unblocked isocyanate groups in elastomers.